1. Field of the Invention
The present invention relates to nonlinear optical chromophores and, more particularly, pertains to second-order nonlinear optical (NLO) polyene-based chromophores sterically stabilized with a dioxine ring and NLO chromophores containing bithiophene derivatives, and devices incorporating the same.
2. Description of the Related Art
Organic second-order nonlinear optical (NLO) materials have recently received increasing attention for applications involving signal processing and telecommunications. Macroscopic nonlinearity of a NLO material is mainly determined by its active component, NLO chromophore which is typically a quasi-linear electron push-pull conjugated molecule having an electron donor group at one end and an electron acceptor group at the other end. Chromophore intermolecular electrostatic interactions prevent the simple scaling of molecular optical nonlinearity into macroscopic optical nonlinearity. Such interactions strongly attenuate the efficient induction of acentric chromophore order (hence, electrooptic activity) by electric field poling or self-assembly methods. Chromophores with xcex2 values many times those of the well-known Disperse Red 19 dye are thus required to obtain electrooptic coefficients comparable to or higher than those of the leading commercial material crystalline lithium niobate.
The value of xcex2 for a chromophore can be increased by using a diene moiety in place of thiophene in the conventional phenylethenylenethiophene xcfx80-conjugated bridge. Moreover, this enhancement in xcex2 can be accomplished without an increase in the wavelength of the charge-transfer absorption xcexmax. However, the resulting phenylpolyene bridge has poor thermal stability unless the polyene structure is locked by a ring structure.
Another effective way of increasing molecular nonlinearity is to extend the bridge with a bithiophene. Traditionally, the bithiophene is incorporated with introducing any side groups on the 3,4-positions of the two thiophene rings. However, the resulting chromophores generally have poor solubility.
A synthetic methodology of a dioxine-locked aminophenylpolyenal donor-bridge, according to the present invention, is described herein. This methodology broadens the scope of polyene-bridged chromophores without sacrificing thermal stability or optical transparency. This synthetic approach facilitates the development of NLO materials possessing EO coefficients as high as 95 pm/V at 1.06 xcexcm and 68 pm/V at 1.3 xcexcm as determined by the attenuated total reflection (ATR) technique.
A variety of different molecular structures are possible for the chromophores of the present invention. An exemplary preferred chromophore according to the present invention includes an aminophenyl electron donor group and a dioxine-containing bridge structure. In a preferred embodiment, the bridge structure also includes at least one bulky side group.
Another exemplary preferred chromophore according to the present invention includes an electron donor group, an electron acceptor group and a ring-locked bridge structure between the electron donor group and the electron acceptor group. The bridge structure comprises a dioxine unit and a bithiophene unit. In a preferred embodiment, the bithiophene structure also includes at least one bulky side group.
Another exemplary preferred chromophore according to the present invention includes an electron donor group, an electron acceptor group, and a bridge structure there between, with the bridge structure including a bithiophene unit. In a preferred embodiment, the bridge structure further includes an isophorone-derived cyclohexene unit.
The NLO materials of the present invention are suitable for a wide range of devices. Functions performed by these devices include, but are not limited to: electrical to optical signal transduction; radio wave to millimeter wave electromagnetic radiation (signal) detection; radio wave to millimeter wave signal generation (broadcasting); optical and millimeter wave beam steering; and signal processing such as analog to digital conversion, ultrafast switching of signals at nodes of optical networks, and highly precise phase control of optical and millimeter wave signals. These materials are suitable for arrays which can be used for optical controlled phased array radars and large steerable antenna systems as well as for electro-optical oscillators which can be used at high frequencies with high spectral purity. Exemplary devices and applications for the NLO materials of the present invention include, but are not limited to: optical phase modulators, Mach-Zehnder intensity modulators, polarization modulators, single side band modulators, modulator cascades, nested modulators, modulator arrays, flexible modulators, electrically controlled optical switches, electrically controlled optical couplers, electrically controlled optical attenuators, optically controlled optical switches, electrically tunable filters, electrically tunable polymer gratings, multiplexers, de-multiplexers, optical cross-connects, optical waveguides for harmonic frequency generation, optical waveguides for sum frequency generation, optical waveguides for difference frequency generation, photonic RF phase shifters, RF quadrature amplification modulators, photonic oscillators based on polymer intensity modulators, time stretching/compression based on polymer intensity modulators, optically controlled phased arrays based on polymer modulators, optical gyroscopes using polymer phase shifters, RF photonic links using polymer modulators, intensity modulators for active mode-locking, optical phase modulators for active mode-locking, optical amplifier gain stabilization based on polymer non-linear optical waveguide devices, and wavelength selectivity/stabilization using polymer non-linear optical waveguide devices.